This invention relates to an apparatus for melting frozen water off of a roof, and specifically to a system which will prevent or melt an ice dam formed on a roof.
An ice dam generally forms along the edge of a roof, possibly in conjunction with a gutter which extends along the roof eaves, or simply at the eaves of a roof. The ice dam forms as a result of water which accumulates on the roof, generally as the result of melting snow, travels along the surface of the roof, or possibly under the roofing material, reaches the edge of the roof and freezes.
It is typical in many parts of the world that two or three feet of snow may build up on a roof. The snow is a fairly good insulator. One way in which ice dams may form is on a roof which has inadequate insulation and is of what is referred to herein as single-roof construction. Any heat loss from the inside of the building will reach the exterior surface of the roof and melt a very thin layer of the snow, forming a snow-water interface between the exterior surface of the roof and the lower surface of the snow. The water does not refreeze because it is insulated by the snow, and proceeds to run down the roof until it reaches the edge of the roof at the eaves. At this point, if the ambient temperature is below freezing, the water will freeze and begin the formation of an ice dam. As water continues to flow down the roof under the snow, it reaches the now-forming ice dam and the dam continues to build in size. In some instances, an ice dam may build up to be a foot or more thick and extend up the roof six to eight feet. The formation of the ice dam prevents run off of water once the snow pack begins to melt, and can result in water being forced up under the roofing material, such as shingles, and, in extreme situations, run down through the roof sheeting under the exterior roofing material into the structure. Additionally, because the water and snow are retained on the roof, the weight build up can result in structural failure.
Such ice dams are, however, not limited to roofs which are not adequately insulted. A double-roof, referred to as a cold roof, is built with a vented air space between the primary roof and an exterior roof. This is supposed to prevent any building heat loss from reaching the exterior surface of the roof and generally is effective to prevent melting at the bottom of the snow layer as the result of escaping heat. However, as the ambient temperature reaches the upper twenties and low thirties (.degree.F.), snow begins to melt along the roof peak, and forms a water interface between the upper surface of the roof and the lower surface of the snow as previously discussed, and forms an ice dam at the eaves of the roof.
Another possible way that an ice dam may form is on a roof which does not overlay an interior structure of the building, but which may abut a vertical south or west facing wall, which is possibly warmed by afternoon sun. Such is the case where a building entry roof or awning is provided, with or without a cold roof design, and the roof exterior surface of the roof is simply heated by conduction from the walls.
Regardless of how an ice dam forms, the presence of the ice dam, icicles and overhanging snow cornices is extremely dangerous to passersby, as they may be struck by falling ice and snow and seriously injured. Additionally, the formation of an ice dam can result in serious structural damage to a building.